Abstract: To cope with the problem that the compatible compression is inefficient for the test set with unbalanced distributed deterministic bits.This paper proposes the following method.First,the test set is formatted according to the multiple scan chains.Then it is divided into several groups by the number of same compatible relations among vectors.And each group does the compatible compression.Next,the results are rearranged and the differences vectors are gained by standard vector difference method.Finally,the differences vectors are compressed using the distance-marking method.This method performs well in compressing the unbalanced distribution of the deterministic bits,and the number of the cyclical scan registers is small.